It is known that commercial and domestic cooling systems, usually employed in the past and still marketed at present, make use of ON-OFF-type conventional compressors. Such compressors have, as a characteristic, the fact of being basically turned on and off at fixed rotation, according to the variation in temperature inside an environment to be cooled.
In order for a compressor to be turned on and off, when necessary, devices called thermostats are used. Thermostats have the function of measuring the variation in operation temperature in the environment to be cooled, and selectively turning on the compressor, if the temperature of the cooled environment exceeds a pre-established upper limit and turning off the compressor, and turning off the compressor if the cooling temperature reaches a pre-established lower limit.
The most widely used thermostat type is the one that makes use of a combination of a bulb containing a fluid that expands with rising temperature, installed so as to be exposed to the temperature inside the environment to be cooled, and mechanically linked to an electromechanical switch that is sensitive to this expansion and contraction of the fluid existing inside the bulb, being capable of turning on and off the switch at predetermined temperatures, according to the application. This switch interrupts the current supplied to the compressor, controlling the operation thereof, keeping the internal environment of the cooling system within pre-established temperature limits.
This type of thermostat is still widely used today, since it has a relatively simple construction and functioning. However, it should be pointed out that these thermostats only make the measurement and switching to turn on and off the compressor according to temperature.
With the technological developments in cooling, conventional compressors of the ON-OFF type are now being exchanged for compressors with higher energetic and cooling efficiency, the so-called variable capacity compressors (VCC). These compressors have, as a characteristic, adjustments in the cooling capacity by varying the velocity of pumping cooling gas, that is, its mass flow, according to the need of the system and its demand for cooling.
The variation in mass flow takes place from a minimum value to a maximum one, such a range of values being proportional to the rotation of the electric motor that drives the variable capacity compressor. The variation in rotation is achieved on these compressors by means of an electronic control called frequency inverter, which adjusts the voltage and frequency applied to the electric motor.
In general, the frequency inverter is provided with a number of electronic circuits with different functions, as for instance a power circuit with incoming stage for filtering electromagnetic interference and a “rectifying-bridge” state for converting an alternating voltage from an external supply source to direct voltage, a control circuit (microcontroller or Digital Signal Processor—DSP), an auxiliary power source for generating internal voltages for other circuits or components of the inverter, a circuit formed by power semiconductors for actuating the electric motor employed on the compressor, among others.
With the development of these new compressors, the simple thermostats of the electromechanical type stopped being used, since they had the limitation of not enabling adjustment of velocity of a variable capacity compressor, the terms only having the function of turning on and off the compressor.
In order to overcome such deficiencies, different types of devices and/or electronic circuits were developed to measure the temperature in a cooled environment and use the data to vary the rotation and, as a result, the mass flow.
For example, the cooling systems use now electronic temperature sensors such as PTC (Positive Temperature Coefficient), which read the temperature inside the cooled environment, compares the value read with pre-defined references and generates a command signal to the electronic control, so that the latter can turn on or off the compressor or can vary the rotation thereof. Other circuits and microprocessors with functioning similar to that of a PTC were developed to overcome the above-cited problems.
Although the PTCs and other circuits or microprocessors are efficient in their functioning, one observes that they have a high cost for implementation as compared to the simple devices of the electromechanical thermostat type. Moreover, one observes that such devices are generally used on cooling systems that make us of variable capacity compressors.
In this regard, what one observes is that such devices do not enable an upgrade in the conventional cooling systems, that is, they do not enable ON-OFF-type conventional compressors to be replaced by variable capacity compressors.
With a view to reduce the costs with devices like PTCs, circuit or microprocessors, and with a view to enable upgrades of the conventional cooling systems, without much adaptation, a solution making use of the simple electromechanical thermostat (common on old coolers), or any other type of thermostat having the function of monitoring the temperature and the switching to actuate the compressor (for instance, an electronic thermostat with relay output), has been developed, as can be seen in FIG. 1.
FIG. 1 illustrates a cooling system comprising a variable capacity compressor 100a, an electronic control 50a having outputs 53a-c for connection to the compressor 100a, a power source 10a, and a simple electronic thermostat 30a. 
One further observes that with this solution the electronic control 50a is a frequency inverter provided with neutral and feed-phase inputs, and a signal input 52a of the thermostat 30a, as will be described later.
In this solution, the power source 10a is linked directly to the feed inputs of the electronic control 50a and a tap 60a is made from the phase wire (connection between the phase of the power source 10a and the input of phase of the electronic control 50a). From this tap, a wire is led to the first terminal of the thermostat 30a and the second terminal of the thermostat 30a is linked to the signal input of the electronic control 50a, such input 52a being referenced internally to the neutral connection of the electronic control 50a. 
The signal input 52a has the main function of checking whether the thermostat 30a is open or closed and to find out whether the compressor 100a should be turned on or off. Such input 52a is linked to an internal circuit comprising, for example, optocouplers, which also have the function of defining the rotation at which the compressor 100a should operate. The rotation is defined by means of data collected from the preceding cycles and stored in volatile memories.
A problem observed during the operation of the system of the solution of FIG. 1 is that, when the thermostat 30a is turned off, the electronic control 50a remains in stand-by, that is, it continues to be fed by the power source 10a and continues consuming energy only for the data of the volatile memory not to be lost. Thus, there is a clear waste of energy, which generates substantially high costs over time.
Moreover, although this solution seeks to reduce costs, what one observes is that the system still uses additional wires, components and cables/wires and so it still substantially reasonable costs if compared with the conventional systems, which used to operate in a simple way and without involving electronics. Another problem is that there are reasonable costs when one uses a volatile memory to store data from previous cycles.
Finally, considering that the electronic control needs to be altered to comprise other electronic components (memories, optocouplers) and wires, what one observes is that the costs in the mounting operation and in the contour conditions, such as test on the client's line, undergoes an impact, which may lead to drop in efficiency of production.